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Hi FreeSurfer Experts,
I had a question regarding contrasts for univariate LME models.
I am interested in looking at the interaction of alcohol with change in volume across two time-points. Included in my model are covariates Gender, ICV, and Previous Drinking History.
My X matrix includes 7 columns: Column 1 = 1s Column 2 = time Column 3 = alcohol Column 4 = time*alcohol Column 5 = Gender Column 6 = ICV Column 7 = Previous Drinking History
My contrast is C = [0 0 0 1 0 0 0 ].
I have 4 different previous drinking history variables. However, when I change column 7 with my different previous drinking history variables, the F and P values for the interaction are the same. Am I setting up my contrasts incorrectly?
Best,
Jessica Hua